We evaluated the relevance of beta 2 microglobulin (B2M) plasma concentration in 109 patients with myelodysplastic syndrome (MDS) from the Duesseldorf registry. Sixty-five patients with B2M level > or =2mg/dl showed a significantly lower overall survival time with a median of 23 in comparison to 61 months for 44 patients with B2M below 2mg/dl. The risk of AML evolution was higher in patients with B2M> or =2mg/dl. Using multivariate analysis we found the B2M level at the time of diagnosis to be an independent prognostic parameter for survival and for the risk of developing AML in high-risk MDS patients.